1. Field of the Invention
The present invention relates to an improvement of a sheet feeding device mounted on an image forming apparatus or the like.
2. Description of the Prior Art
For example, an image forming apparatus such as a copying machine or a printer requires sheets (transfer paper, sensitizing paper, thermosensible paper or the like) on which an image is formed. A sheet feeding cassette detachable from the main body of the apparatus has been known as a device for feeding the sheets.
The sheet feeding cassette can contain a plurality of sheets. When the sheet feeding cassette is mounted on the image forming apparatus, the sheets are fed one at a time by a feed roller provided in the main body of the apparatus. In order to feed the sheets by the feed roller, supply pressure must be applied to the sheets with front ends of the sheets pressed to the feed roller. If supply pressure is applied, the friction force is produced between the feed roller and the sheets. The sheets can be fed by rotating the feed roller in the state.
Accordingly, in order to apply supply pressure to the sheets, the sheet feeding cassette is generally provided with a mounting plate 1, as shown in FIG. 1. The mounting plate 1 is so adapted that its forward portion can be moved up and down centered with respect to its rear end and is urged upward by a spring 2. Since the sheets contained in a cassette case 3 are mounted on this mounting plate 1, the front ends of the sheets are pushed upward by the mounting plate 1 to be brought into contact with a feed roller 4.
A non-slip pad 5 having a high coefficient of friction is affixed to an upper surface of the forward portion of the mounting plate 1. The non-slip pad 5 is affixed in such a position that it comes into contact with the feed roller 4 when there remain no sheets. The non-slip pad 5 is used for holding the friction force between the sheets and the mounting plate 1 when there remain a few sheets on the mounting plate 1 to prevent the remaining sheets from being fed at one time.
The foregoing will be described in more detail. It is assumed that the non-slip pad 5 is not provided on the mounting plate 1. In this case, the friction force between the last sheet and the mounting plate 1 is smaller than the friction force between the sheets. Accordingly, if there remain a few sheets, for example, there remain five or six sheets, the situation is often encountered where no slip occurs between the sheets where the friction force is large but slip occurs between the last sheet and the mounting plate 1 where the friction force is small so that five or six sheets are fed at one time.
Consequently, the non-slip pad is an indispensable member to prevent, when there remain a few sheets, the remaining sheets from being fed at one time.
However, the conventional sheet feeding cassette having the above described non-slip pad has the disadvantage in that buzzing noise is liable to be produced in feeding the last sheet.
Buzzing noise is mainly produced by friction between the non-slip pad and the last sheet. Accordingly, if the non-slip pad 5 is eliminated, no buzzing noise is produced. However, when there remain a few sheets in the sheet feeding cassette, the remaining sheets are liable to be fed at one time, as described above.
Therefore, the non-slip pad cannot be eliminated. Accordingly, it is desired to prevent buzzing noise from being produced with the non-slip pad being left.